For example, a patent document 1, which corresponds to Publication of U.S. Pat. No. 5,497,754, discloses a known sealed tank system. The sealed tank system includes a valve device, which is equipped to a communication passage, which communicates with a fuel tank, to constitute a sealed structure of the fuel tank, to restrict fuel from flowing out from the fuel tank to the atmosphere, in view of avoidance of air pollution. In the sealed tank system of the patent document 1, a pressure control valve is equipped between the fuel tank and a canister, in order to avoid breakage of the fuel tank and/or the like due to change in the pressure of the fuel tank.    (Patent Document 1) JP-A-H7-217504
It is noted that, in the patent document 1, the pressure control valve is opened, during an engine is in operation, only when the pressure of the fuel tank increases beyond a predetermined positive pressure value or decreases below a predetermined negative pressure value. It is assumable to employ the configuration of the patent document 1 in a vehicle, such as a plug-in hybrid car (PHV), in which an engine is seldom activated. In such a case, the valve may not be activated for a long time period. Consequently, the valve may cause seizure.